The invention relates to a method for regulating a clutch or a brake in an electrohydraulically controlled transmission.
An automatic transmission for a motor vehicle usually has several clutches and brakes with which different gear steps and the direction of travel can be shifted. In such automatic transmissions there is customarily used as starting element a hydrodynamic torque converter which, to optimize the total efficiency of the transmission, is provided with a converter lock-up clutch which in certain gear steps is partly or totally closed depending on rotational speed and load of the driven engine.
There are known also special wet operating starting clutches which can also be integrated in the automatic transmission. But those starting clutches are mostly situated as unit on the transmission input, for ex., also as starting element in an automatic continuously variable transmission. The wet starting clutch is also disposed as unit on the transmission output, specially in CVT transmissions (continuously variable transmissions).
The clutches and brakes in the automatic transmission or in the automated continuously variable transmission are usually electrohydraulically controlled independently of the application of the shifting element as gear-change clutch, starting clutch, or converter lock-up clutch. For this purpose variables according to specifics of the vehicle, specifics of the transmission and driving mode such as axle and gear ratios, transmission oil temperature, engine torque, engine rotational speed, vehicle speed, internal rotational speeds of the transmission, accelerator pedal position and accelerator pedal change, brake signal, vehicle acceleration, tractional resistance and driver activity are processed in an electronic transmission control unit and corresponding output signals relevant to the clutch, for ex., for pressure control or pressure regulation, or during a gear change or for rotational speed regulation during a slip operation, are transmitted to a hydraulic control unit and there converted by means of actuators and hydraulic valves into hydraulic pressure for the corresponding clutch.
Gruhle, Jauch, Knapp and Ruchardt describe as effective example in VDI Reports No. 1175, 1995, a method for model-supported application of a regulated converter lock-up clutch in automatic transmissions of passenger cars. The converter lock-up clutch and the control thereof are at present a sub-system in the automatic transmission which decisively imprint the driveability of a vehicle. To meet the increasing requirements in comfort, driving performance and fuel consumption, here is proposed a complex control draft of the converter clutch provided with a control loop which works with the differential rotational speed from engine and turbine rotational speeds. To stabilize and increase the dynamics of the control loop, there are implemented in addition a load modulation of the engine torque and special functions with direct pressure standards for the converter lock-up clutch.
In its basic structure the control draft described by way of example is applicable to all electrohydraulically actuated clutches and brakes in transmissions of passenger cars and is not confined to the case of the converter lock-up clutch. But disadvantages in such a complex control draft are the basic structure of the software of the electronic transmission control which is vague due to added functionalities and can be extended only at great expense, and the considerable cost for application of such functions.
Therefore, the problem on which this invention is based is, departing from the cited prior art, further to develop with regard to improved control quality and control dynamics and reduced application cost, a method for regulating a clutch or brake designed for ex., as gear clutch, starting clutch or converter lock-up clutch.
According to the invention this problem is solved by the features of claim 1. Other developments of the invention result from the sub-claims.
The invention accordingly proposes to design the clutch regulation with a model-based compensation pressure regulator using an observation unit of interference level which, based on a drive train model, estimates interference levels of the clutch regulation according to a condition-estimation method. The interference levels reproduce the inaccuracies in comparison with the real system of the physical mathematical model used according to regulation technology and result, specially from characteristic line errors determined by principle, in stationary and dynamic control errors, hydraulic tolerances, the same as dynamic model errors determined by principle.
Therefore, the observation unit estimates from the drive train model the interference torque on the clutch or brake to be shifted or regulated and the load torque cropping up in power flow direction behind the clutch or brake. According to the configuration of the drive train model, the characteristic shape of the torsional oscillations of the drive train can also be estimated.
The inventive method is based on a non-linear compensation method according to the principle of exact linearization. From the linkage of a hydraulics model of the clutch control with an inverse model of the control system, a simple transmission function results. The remaining system can be drafted by control technology according to the linear theory specially by a separation of the non-linear portion of the observation unit.
By such a regulation draft of the clutch constructed as compensation pressure control loop supported by observation unit, there are obtained specially advantageously an operating-point dependent, uniform control behavior of the closed control loop with high adjusting dynamics resulting therefrom and a strong sequence and interference behavior.
In a first development of the invention it is proposed to design the interference-level observation unit as reduced observation unit which estimates only the unknown system variables relevant for the clutch regulation. Hereby is advantageously obtained as high as possible a computer speed and therewith as high as possible regulator dynamics.
In a second development of the invention it is proposed to design the interference-level observation unit as complete observation unit which estimates all system variables. Hereby can be advantageously improved in particular a servo-control quality for the regulator and therewith the quality of the regulator.
In a third development of the invention it is proposed to design the interference-level observation unit as Kalman filter which is advantageously sturdy in relation to signal rustles.
In another development of the invention it is proposed to design as several linked regulation blocks the regulator of the closed, model-based and observation-unit supported compensation pressure control loop. A first block processes as rotational speed regulator the rotational speeds and slip standards of the clutch regulation. The rotational speed regulator advantageously does not need to contain components for ensuring stationary precisions and can be designed as simple P regulator. A consecutive second block calculates from the theoretical standards of the rotational speed regulations, from the servo-control values of the inverse system model and from estimated interference levels of the observation unit, a pressure standard for the hydraulic servo component of the clutch control. The conversion independent of the operating point of the regulated quantity is advantageous here. A consecutive third block compensates as pressure regulator the tolerances of the hydraulic servo component with the aid of estimated variables of the observation unit and delivers a theoretical pressure for the clutch control. By the compensation of the technical pressure fluctuations of customary pressure adjusters in the whole operating range, the dynamics of the control loop is clearly improved. A consecutive fourth block works as traditional pressure-current regulator and converts the theoretical pressure standard into a current standard for the electrohydraulic pressure adjuster.
In one other development of the invention it is proposed to design the rotational speed regulator of the closed, model-based and observation-unit supported compensation pressure control loop as PD regulator with additional non-linear term. In case of great divergences from a theoretical value, a quicker approximation to the theoretical value is hereby achieved.
In another development of the invention it is proposed to design the pressure regulator of the closed, model-based and observation-unit supported compensation pressure control loop as regulator with PT2 characteristic according to the principle of exact linearization. The dynamics of the control loop can be advantageously influenced hereby.
The inventive regulation draft at the same time can be universally used for every electrohydraulically controlled clutch. Cases of application are, for ex., a wet starting clutch in an automatic transmission or in an automated manual transmission without or with stand-by control SBC, a selector clutch or selector brake in an automatic transmission or a converter lock-up clutch in an automated transmission.